Just recently upgraded to 13.04 and am having trouble running TF2 via Steam. Whenever I start Steam I get a dialog saying:

OpenGL GLX context is not using direct rendering, which may cause performance problems.

Every time I go to launch TF2 I get a dialog saying:

Could not find required OpenGL entry pint 'glGetError'! Either your video card is unsupported, or your OpenGL driver needs to be updated.

I tried updating my Nvidia drivers, hoping that would solve this issue but alas, it did not. I believe this issue is related to a fix I used to get Skype working with 13.04, specifically this. Just a heads up I'm using GNOME Shell 3.8.